Hardness Tests And Charpy Impact Test

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  • Topic: Vickers hardness test, Rockwell scale, Hardness
  • Pages : 10 (2289 words )
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  • Published : November 25, 2012
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TITLE
Hardness Tests And Charpy Impact Test
OBJECTIVE
1. To compare the hardness of the carbon steel, mild steel and ASSAB steel using three different hardness tests, which are Vickers Hardness Test, Rockwell Hardness Test and Brinell Hardness Test. 2. To study the hardness of mild steel, carbon steel and ASSAB which is an important in engineering to design structures or components that related in mechanical properties

3. To determine the resistance of carbon steel and mild steel against sudden impact by Charpy Impact Test.

INTRODUCTION

Hardness is a measure of a material’s resistance to localized plastic deformation. It also is one of the important properties to be considered. Mechanical properties of metals are a vital of engineering to design the components which using predetermined materials such that unacceptable levels of deformation and failure will not occur.

Hardness is a resistance of properties of material to permanent (plastic) deformation caused by steel ball or pyramid-shape diamond when it is pressed onto its surface. There will be three basic method of Hardness Test that will be carried out on carbon and metal: (a) Vickers Test

(b) Rockwell Test
(c) Brinell Test

THEORY

1. Vickers Test
VHN = Applied load / Surface area of depression
=
= 1.854 P/ d2 (approximate)
Where P = applied load (kgf)
d = (d1+ d2) / 2 (mm)

2. Rockwell Test
HRC = 100 – d /0.002
HRB = 130 – d /0.002
Where d = depth of the indentation

3. Brinell Test
BHN = Applied force / curve area of indentation
P / D/2 [D - (D² - d²)]
= P / Dh

WhereP = applied load (kgf) D = diameter of steel ball (mm)
d = diameter of resulting indentation (mm)
h = depth of indentation (mm)
= ½ [D - (D² - d²)]

APPARATUS
1. Set of Vickers Hardness Test Machine
2. Set of Rockwell Hardness Test Machine
3. Set of Brinell Hardness Test Machine

SPECIMENS
Mild steel, carbon steel and ASSAB steel

A) VICKERS HARDNESS TEST
From this method square shape pyramid diamond 136° was press to surface of metal using some load (5kgf until 120kgf) under certain time (15 sec) and lastly the load will release. Square shape corner on the metal surface will be used.

To obtain the value of hardness, Vickers Hardness Number (VHN) is calculated as below:

VHN=Mass of the loadSurface area of depression
=2PSin136°2d2
=1.854Fd2approximately
Where, P=applied forcekgf
d=d1+d22
B) ROCKWELL HARDENESS TEST
This method has 2 main scales which are:
a) Scale B, concavity is a steel ball (1.58 mm∅) and load using is 100 kgf. b) Scale C, concavity is a cone diamond having corner 120° and load is 150 kgf.

Rockwell hardness (HR) can be calculated as equation below:
HRC=100-d0.002
HRB=130-d0.002
Where d=concavity

C) BRINELL HARDNESS TEST
From brinell hardness test, the harden steel ball has good diameter, D under the load and certain time will be use to get diameter concavity effect,d. BHN=LoadArea of concavity
=PD2D2-d2
=PπDh

Where, P=loadkgf
D=diameter of the steel ballmm
d=diameter concavity effectmm
H=internal concavity effectmm
=12D-D2-d2

PROCEDURE
a) Vickers Hardness Test

1. The specimen (Mild Steel) is put on the anvil of the Vickers hardness machine precisely. 2. The sample is focused until the lines on the surface of the sample can be observed clearly. 3. The focal lens of the microscope is turned to the indenter. 4. The indenter is then pressed into the sample.

5. The test force is maintained for a specific dwell time of about 15 seconds. 6. The indenter is...
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